Perhaps surprisingly, most of the patients suffered relatively minor injuries, such as bruises and scratches or the loss of a finger or toe.

"About half the patients went home right away," said study leader Amber Guth, a professor of surgery at the center.

But a quarter of the patients had at least one arm or leg amputated and one person lost all four limbs. The limbs were either severed by the train itself or were so mangled that they had to be amputated.

About 10 percent of the patients died in the hospital from their injuries.

Eighty percent of the patients were male and the average age was about 39 years old.

Most at risk

The study found that subway injuries were associated with the city's rates of unemployment and homelessness.

The highest number of subway injuries occurred during the early and late years of the study, when the city's economy was weak.

From 2000 to 2003, 25 of 56 patients treated were unemployed, and one quarter of the injuries came from suicide attempts.

Between 1994 and 2000, a period of economic improvement, accident rates declined.

The study also indicates that a high percentage of those involved in subway injuries were mentally impaired.

Of the surviving patients, about 35 percent of them were discharged to psychiatric or rehabilitation services.

"People who are injured often are very marginal people, with less economic resources and a lot of psychiatric issues," Guth said.

Preventing injuries

The simplest solution for preventing subway injuries is to construct a barrier between passengers and the tracks, as is done in Hong Kong. But this would be prohibitively expensive, since New York City's subway system is more than a century old.

An alternative solution that could be easily implemented, the researchers say, would be to have trains reduce their speeds when entering stations.

Incoming trains enter stations at about 30 mph. By slowing down, the drivers would have more time to notice people on the tracks and stop before impact. Also, any injuries that did occur would be less severe.

The researchers also suggest that police officers and transit workers be trained to spot behaviors that are associated with suicide attempts, especially during periods of economic downturn in the city.